Realized and Unrealized Investment Gains and Losses (Realized and Unrealized Investment Gains (Losses) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Workers' Compensation Discount, Percent		0.00%
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, No Previous Impairment				$ 0
Fixed maturity securities, Gains		$ 72,215,000	$ 23,755,000	39,113,000
Fixed maturity securities, Losses		(6,434,000)	(4,065,000)	(4,420,000)
Investment funds		58,861,000	93,529,000	96,204,000
Gain (Loss) on Sale of Properties		7,757,000	0	85,659,000
Gain (Loss) on Sale of Other Investments		138,519,000	2,775,000	0
Other (1)		134,900,000
Net realized gains on investments sales		285,119,000	125,633,000	254,852,000
Other than Temporary Impairment Losses, Investments		18,114,000	33,309,000
Net other-than-temporary impairments		(18,114,000)	(33,309,000)	0
Equity securities available for sale		14,201,000	9,639,000	38,296,000
Net investment gains		267,005,000	92,324,000	254,852,000
Income tax expense		(93,452,000)	(32,313,000)	(89,198,000)
Total after-tax investment gains		$ 173,553,000	60,011,000	$ 165,654,000
Preferred stocks
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Other		one
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, No Previous Impairment	$ 13,400,000
Common Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Other		two
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, No Previous Impairment		$ 18,100,000	10,900,000
Fixed Income Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, No Previous Impairment			9,000,000
Equity securities available for sale
Schedule of Available-for-sale Securities [Line Items]
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, No Previous Impairment		$ 18,100,000	$ 24,300,000
Weighted Average
Schedule of Available-for-sale Securities [Line Items]
Workers' Compensation Discount, Percent		0.00%